Pre-upstream review hardening:
- /accounts + /accounts/test now reject private/internal IMAP/SMTP hosts via
isPrivateIP(), matching /config + /incoming-config (SSRF).
- QueueDetail body iframe uses sandbox="" (script-less, no same-origin) like the
inbound pane, instead of allow-same-origin.
- /send sanitizer drops the <style> tag + data: scheme to match the stricter
inbound sanitizeBody allowlist.
- Per-account SMTP transport sets tls.rejectUnauthorized explicitly.